The present invention relates to an apparatus for the chemical metallization of previously activated porous substrate webs of foams, nonwovens, needle felts, of plastic material having a porosity of 45 to 98% of the substrate material.
The chemical metallization of plastic surfaces in particular is constantly becoming more widespread. It may be that, in automobile construction, certain plastic parts are to be given a decorative exterior by the application of a metal layer. Often, in the fabrication of household articles, tools, machines for work and for everyday use, a plastic part is to be protected on its surface by a metal layer or metallized for some other reason. This means that, with a very large number of consumer goods of every type and function, currently it appears to be economically attractive to combine the advantages of plastic bodies with respect to weight, shaping, damping, physical properties, price etc. with metallic properties, such as, for example, gleam, magnetism, electric conductivity, thermal conductivity or shielding effect, by the application of a metallic layer to the plastic surface.
However, such plastic surfaces cannot just be coated with a metal layer. Rather, it is common practice that, following a suitable pretreatment matched to the specific function of the component or workpiece to be metallized, the plastic surface is activated. The pretreatment may involve, for example, cleaning, roughening, etching, coating or the like, whereas the stated activation of the plastic surface is to be understood as its coating with a catalytically active substance. During the course of the activation, catalytically active particles based on Pd/Sn come to be deposited particularly frequently. Other activation methods, free from precious metals, are known but are clearly in the minority in terms of the quantity processed.
Once activation of the surfaces of the textile substrate has taken place, the chemical metallization of the activated substrate surface is subsequently carried out. For this purpose, the substrate is usually immersed in a metallization bath, such baths being based on copper, silver and nickel, with nickel being preferred.
The preparation and the composition of such activation solutions are known, for example from German Auslegesschrift 1,197,720 or German Offenlegungsschrift 2,743,768. A great variety of metallization solutions are likewise known to persons skilled in the art. Along with complexing agents and agents for adjusting the pH, normally the metallization solutions principally contain a dissolved salt of the metal to be deposited as well as a reducing agent. Usually sodium hypophosphite or sodium borohydride, also alkylaminoboranes or formalin, are used as a reducing agent.
Following the pretreatment, activation and chemical metallization steps, then (if desired) the metal layer present on the plastic surface is further reinforced by galvanic means. This is done either with the same metal as in the metallization or another metal or a metal alloy, until finally the plastic part has on its surface the desired metallic properties.
It is also known to make porous plastic substrates surface-conductive by graphitizing or vapor-depositing metals and subsequently subjecting them to a multi-stage treatment in electroplating baths (German Offenlegungsschrift 1,696,090). It is also known from this specification to remove the particles of liquid remaining in the pores of the substrate web by means of a suction-removal apparatus after electroplating. Also, according to German Offenlegungsschrift 2,844,708, a non-conducting porous strip can be made electrically conductive in order to electroplate it subsequently in a multi-stage process. The methods specified in these two specifications require very complex apparatus and a great expenditure of time.
Copper and nickel are the favored metals in chemical metal deposition on plastic surfaces in the industrial sector. Some references which discuss pretreatment, activation and chemical metallization are, for example, "Kunststoff-Galvanisierung" (Plastic Electroplating), E. Leuze Verlag, (Saulgau) and General Methods of Galvanic Metal Deposition from the "Handbuch der Galvanotechnik" (Electrodeposition Manual), volume 1-4, published by H. W. Dettner/J. Elze, Carl Hanser Verlag Munich 1964.
Today, the technique of chemical metal deposition on plastic surfaces does not generally present a problem. However, a manufacturer desires to produce the required metallic properties on the plastic surface, such as gleam, hardness, adhesive strength, economically viably with chemicals which are, as far as possible, environmentally compatible and harmless from the aspect of industrial medicine.
Problems occur in chemical metallization only when plastic materials which are highly porous and consequently have a relatively great surface area, such as open-pored foams, needle felts, nonwovens or other textile materials are to be chemically metallized after their activation. The enormously large surface of these plastic bodies in their highly porous configuration of 45-98% porosity, with up to several square meters of surface per g of processed plastic, means that, in chemical metallization, large quantities of gas are liberated in a short time by the accompanying evolution of hydrogen. With the reliable removal by suction of large quantities of hydrogen already being a task in itself, it is additionally hampered by the further heating of the metallization solution, observed in chemical metallization. This causes vapors to form over the solution, which are in themselves already harmful to health and are further increased in their harmful potential by entrained minute particles of metal. The consequence of this is that the entire metallization system has to be equipped with a complex and expensive suction-removal system, which of course burdens the cost-effectiveness of the chemical metallization process. The chemical metallization of such highly porous plastic webs is discussed in German Patent Specification 3,710,895.
An object of the present invention is to provide a space-saving apparatus for the chemical metallization of previously activated open-pored substrate webs of foams, nonwovens, needle felts of plastic or textile material, in particular having a porosity of 45 to 98% of the substrate material, in order to subject these substrates to a chemical metallization in a technically easily manageable manner. This should be done economically yet with good technical properties with respect to subsequent processing of the material bringing the substrate webs into contact with the chemical metallization solution; chemical metallization of the substrate web; and centrifugal throwing off of used and/or excess chemical metallization solution once chemical metallization of the substrate web has taken place.
Another object of the present invention is to optimize the working cycle of the three individual working steps listed above. These steps all require working times of different lengths. The optimization should allow a continuous production of metallized nonwoven or needle-felt webs or open-pored foams with minimal labor expenditures.